Obama adviser Jason Furman has famously claimed that Walmart, the largest U.S. retailer and the largest private employer in Pennsylvania and many other states, saves poor Americans $50 billion a year by selling groceries more cheaply than other chains.

How? Walmart buys in enormous bulk; and it doesn't have to pay union pensions and healthcare, among other old-line grocery expenses.

The claim that Walmart helps the poor has been used to socially justify Walmart's low wages.

But, writing for Reuters, bond-watcher Cate Long pokes holes in Furman's widely-quoted number by pointing out, among other things, that total Walmart grocery sales are less than $75 billion/year.

As lead grocery shopper for my family of 8, I can testify that Walmart sometimes has excellent prices for canned herring and other packaged goods, but its meat and produce prices are not competitive with my local Shop-Rite. Long says Walmart's former pricing advantage has eroded.